(a) Field of the Invention
The present invention relates to an electric power generation control method during idle charge in a hybrid electric vehicle (HEV). More particularly, the present invention maintains an engine load at an appropriate level by adjusting the amount of power generation depending on an altitude correction coefficient, controls a generation load and RPM depending on whether or not an air conditioner operates and based on a gear shift position, and corrects the RPM by inputting a correction value for the amount of power generation, if an actual RPM drops below a reference value in preparation of a target charge RPM.
(b) Background Art
The term “hybrid vehicle,” in its broadest sense, refers to a vehicle that utilizes at least two different kinds of power sources. Usually, the term refers to a vehicle that uses fuel and an electric motor, driven by a battery. Such a vehicle is more precisely called a hybrid electric vehicle (HEV).
The hybrid electric vehicle can take on many various structures. Most hybrid electric vehicles are either parallel type or series type.
The parallel type hybrid electric vehicle is configured such that the engine charges the battery and also directly drives the vehicle together with the electric motor. Such a parallel type hybrid electric vehicle has a shortcoming in that its structure and control logic are relatively complicated compared to the series type. Nevertheless, since this parallel type hybrid electric vehicle is efficient in that it utilizes the mechanical energy of the engine and the electric energy of the battery simultaneously, it is widely adopted in passenger cars, etc.
A typical hybrid electric vehicle is equipped with a hybrid control unit (HCU) for controlling the overall operation of the vehicle. For example, the HCU includes an engine control unit (ECU), a motor control unit (MCU), a transmission control unit (TCU), a battery management system (BMS), a full auto temperature controller (FATC) for controlling the interior temperature of the vehicle and the like.
These control units are interconnected via a high-speed CAN communication line with the hybrid control unit as an upper controller so that they mutually transmit and receive information.
In addition, the hybrid electric vehicle includes a high voltage battery, or main battery, for supplying the driving power of the electric motor. The high voltage battery supplies a needed power while continuously charging and discharging during driving.
The high voltage battery supplies (discharges) electric energy during the motor assist operation and stores (charges) electric energy during regenerative braking or engine driving. The battery management system (BMS) transmits the battery state of charge (SOC), available charge power, available discharge power, etc., to the HCU/MCU to perform safety and lifespan management of the battery.
A typical hybrid electric vehicle performs motor assist continuously when driving uphill at high altitudes. The SOC is therefore lowered to a minimum level that the high voltage battery can control. Electric power is generated to prevent the SOC from being lowered, and the motor assist and charge are repeated in accordance with the SOC. However, if the SOC reaches the minimum level, electric power is generated continuously to recover the SOC.
Accordingly, the power corresponding to the maximum capacity of the engine is taken and transmitted to the high voltage battery for the recovery of the SOC as soon as possible.
Moreover, during idle, the electric power is also generated to recover the SOC. The power corresponding to the maximum value of idle torque is used for this generation.
However, in the conventional method, the engine transmits the power to the motor even if the air conditioner is turned on or if other loads are applied to the engine. This is a problem when driving at high altitudes, because, for example, if the air conditioner is turned on, a greater power is needed. In this case, if the same amount of generation as is used at sea level is generated, it may exceed the allowable power of the engine, thus causing engine stall.
As less oxygen is available at high altitudes, the engine power is reduced. If the electric power is generated to the same extent as at sea level, a load higher than the engine output is applied to the engine, thus causing a risk of engine stall.
Accordingly, it is necessary to set the generation amount within the allowable capacity of the engine while charging the high voltage battery in the hybrid electric vehicle and, especially, to improve the method for setting the generation amount and for controlling the charge at high altitudes.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.